ldtp: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/ldtp - from package: ldtp

You may install the required package with command apt-get install {package}

Error in other languages:
ldtp: bevel nie gevind nie
ldtp: comandă negăsită
ldtp: comando não encontrado
ldtp: commande introuvable
ldtp: command not found
ldtp: käsku ei ole
ldtp: không tìm thấy lệnh
ldtp: komanda nerasta
ldtp: Kommando nicht gefunden.
ldtp: kommandot finns inte
ldtp: komut yok
ldtp: nie znaleziono polecenia
ldtp: níor aimsíodh an t-ordú
ldtp: no se encontró la orden
ldtp: no s'ha trobat l'ordre
ldtp: opdracht niet gevonden
ldtp: parancs nem található
ldtp: perintah tidak ditemukan
ldtp: príkaz nenájdený
ldtp: příkaz nenalezen
ldtp: команда не найдена
ldtp: командата не е открита
ldtp: 命令找不到
ldtp: コマンドが見つかりません